Method of producing a heat exchanger

ABSTRACT

A heat exchanger includes a rectangular housing consisting of four lateral walls and closely receiving a heat-transfer corrugated sheet. Two heat-exchange gases flow at the respective opposite surfaces of the sheet in the furrows defined by the sheet and are supplied to and discharged from the furrows via apertures through two opposite walls of the housing. Plate-form sealing elements of refractory material are caused to press firmly against respective opposite corrugated edges of the sheet by plate-like end members closing the ends of the housing and a spring disposed between one end member and the nearer sealing element.

llite States Ptet Kanzler et a1.

[ Aug. 20, 1974 METHOD OF PRODUCING A HEAT EXCHANGER Inventors: llllansJoachim Kanzler, Viernheim;

Hans Aupor, Mannheim, both of Germany Motoren-Werke Mannheim AG Vorm.Benz ABT Stationarer Nlotorenbau, Mannheim, Germany Filed: July 11, 1973Appl. No.: 378,328

Assignee:

US. Cl.... 29/1573 1), 29/157.3 R, 113/118 D, 165/166 Int; Cl 321d53/02, B23p 15/26 Field of Search. 165/166; 29/1573 D, 157.3 R; 113/118D, 118 R References Cited UNITED STATES PATENTS 2,953,110 9/1960Etheridge 165/157 X 2,958,935 11/1960 Bloem 3,211,219 10/1965 Rosenblad165/166 3,372,453 3/1968 Butt 29/1573 R 3,601,185 8/1971 Rothman 165/1663,787,944 1/1974 Mittman 29/1573 R Primary ExaminerCharles W. LanhamAssistant Examiner-D. C. Reiley, lll

Attorney, Agent, or FirmWaters, Roditi, Schwartz & Nissen [5 7 ABSTRACTA heat exchanger includes a rectangular housing consisting of fourlateral walls and closely receiving a heat-transfer corrugated sheet.Two heat-exchange gases flow at the respective opposite surfaces of thesheet in the furrows defined by the sheet and are supplied to anddischarged from the furrows via apertures through two opposite walls ofthe housing. Plate-form sealing elements of refractory material arecaused to press firmly against respective opposite corrugated edges ofthe sheet by plate-like end members closing the ends of the housing anda spring disposed between one end member and the nearer sealing element.

1 Claim, 7 Drawing Figures PATENTEBauszo 1974 f 3.829.945

sum 2 or 3 METHOD OF PRODUCING A HEAT EXCHANGER BACKGROUND OF THEINVENTION 1. Field of the Invention The invention relates to a heatexchanger, more particularly an air preheater.

2. Description of the Prior Art A heat exchanger is known having aheat-transfer wall in theform of a corrugated metal sheet whereof thefolds are through l80 each time. With its housing, this sheet forms ablock-shaped assembly which also includes inlet and outlet apertures forthe two heat exchange media. The furrows are closed at the ends of theassembly, at which the corrugated edges of the sheet are situated, bywelded or soldered joints to separate the two media. This can be carriedout either by butt soldering of cover plates to the corrugated edges, orby soldering-in spacers between the folds, or by bending the sheet tobring together its corrugated edges and then welding them together. Sucha construction is shown for example in German Patent Specification No.1,111,221, FIGS. 2 and 3.

The aforedescribed welding or soldering involve a considerable amount ofwork. A further important disadvantage is that there is a markedtendency to form cracks at the joint zones owing to the unavoidablethermal stresses between the corrugated sheet and the soldered-on coverplates or soldered-in spacers or at the welded-together corrugatededges, since the rigid joints produced cannot sufficiently take up thestresses which occur by deformation.

SUMMARY OF THE INVENTION According to one aspect of the presentinvention there is provided a heat exchanger, comprising a corrugatedmetal sheet which forms a heat transfer wall, portions of one surface ofsaid sheet bounding a first group of furrows which furrows alternatewith folds in said sheet, first inlet means communicating with saidfirst group of furrows for supplying a first fluid medium thereto, firstoutlet means communicating with said first group of furrows forreceiving said first fluid medium therefrom, portions of the oppositesurface of said sheet bounding a second group of furrows which furrowsalternate with other folds in said sheet, second inlet meanscommunicating with said second group of furrows for supplying a secondfluid medium thereto, second outlet means communicating with said secondgroup of furrows for receiving said second fluid medium therefrom,sealing elements contacting respective opposite corrugated edges of saidsheet, and means urging said sealing elements to press firmly againstsaid corrugated edges, said urging means comprising platelike endmembers disposed near to therespective corrugated edges of said sheet.

According to another aspect of the present invention, there is providedin a method of producing a heat exchanger comprising a corrugated metalsheet which forms a heat transfer wall, the steps of inserting spacersinto furrows alternating with folds of said sheet but so as to leavesaid folds exposed, clamping together said spacers with theinterposition of said sheet, and pressing portions of said folds inwardssimultaneously with bar-like tool to form at said folds projectingportions of said sheet which serve to maintain the width of saidfurrows.

The arrangement whereby the end members urge the sealing elements topress firmly on the corrugated edges of the sheet has the advantages ofdispensing with expensive welding or soldering work at these edges andof providing the possibility of relative movement between the sheet andthe end members, so that thermal stresses liable to produce cracking nolonger occur.

If the heat exchanger is used as an air preheater for thecombustion-supporting air of heating burners, e.g. of hot gas engines,the heat exchanger must be capable of withstanding temperatures of up toabout 700C. Advantageously, it is made capable of doing this by using asthe sealing elements plate-form sealing elements consisting of felt-likerefractory material. The felt-like property compensates for smallirregularities in the corrugated edges and thus provides a satisfactoryseal.

To prevent the plate-form sealing elements from being cut by sharpcorrugated edges of the sheet, the sealing elements can advantageouslybe provided with an internal insert consisting of a refractory wiregauze.

The strength of the plate-form sealing elements can also beadvantageously improved by coating the sealing elements with a hardeningrefractory substance at least at its major face directed towards thecorrugated sheet.

The sheet is advantageously connected to a housing of the heat exchangerwithout the use of soldered or welded joints. This is achived byinserting the sheet in a housing which consists of four lateral wallsarranged in the form of a rectangle and opposite walls of which areformed with inlet and outlet apertures providing the inlet and outletmeans, these walls otherwise closing-off the furrows. For this latterclosure, it is sufficient to have metal-to-metal lines of contactbetween these walls and the sheet folds, since it is not necessary tohave a complete seal at these regions, because the same medium ispresent at both sides of each line of contact.

The sealing of the other, i.e. non-corrugated, edges of the sheet, whichextend parallel to the folds, is advantageously also effected withoutsoldered or welded joints by arranging that the two other walls of thehousing, together with in each case a lip plate, embrace thenon-corrugated edges of the sheet with the interposition of sealingelements of U-shaped cross-section also embracing those edges.

The pressing of the corrugated edges of the sheet on the sealingelements is conveniently brought about by subjecting the sealingelements to the pressure of one or more springs. In this way, the sheetcan expand freely in the direction of its folds without any dangerousstresses taking place.

In order to reduce the risk of the spring force slackening under theaction of heat, the spring or springs is- /are situated advantageouslynear the colder corrugated edge of the sheet.

For maintaining the width dimensions of the furrows in a satisfactorymanner and to improve the shaperetaining ability of the assembly, thesheet can be provided with indentations and correspondingspacemaintaining projections.

It is also possible to achieve this object by maintaining the furrowwalls spaced from one another by portions which are widened transverselyof the folds and are produced by pressing the folds inwards from theoutside. When this is carried out, the metal sheet material of each foldyielding transversely to the fold, comes into contact with theneighbouring portions of the nearest folds and thus ensures that thenecessary spacing is maintained.

This spacing arrangement can advantageously be ensured with a minimum ofsheet deformation by arranging the widened portions in rows which extendat right angles to the folds.

These widened portions can be produced in a simple an inexpensive mannerby means of a bar-shaped tool with which the folds are pressed-inlocally, the remainder of the sheet being held in position by means ofspacer plates which are held together by clamping means and leave thefolds free.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may beclearly understood and readily carried into effect, reference will nowbe made, by way of example, to the accompanying drawings, in which:

FIG. 1 shows a perspective diagrammatic view of a corrugated sheet and ahousing of a heat exchanger.

FIG. 2 shows a diagrammatic section taken on the plane Il-ll of FIG. 1,

FIG. 3 shows a diagrammatic section on the plane III- III of FIG. 1,

FIG. 4 shows the heat exchanger partly broken away and in perspectivediagrammatic view,

FIG. 5 shows a horizontal section through a vertical edge region of thehousing,

FIG. 6 shows a fragmentary perspective view of a modified version of thecorrugated sheet, with pressedin widened portions, and

FIG. 7 shows a method of producing the widened portions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 to 5, theheat exchanger has a heat-transfer wall in the form of a corrugatedmetal sheet 1 whereof the folds 2 and 3 are through 180 in each case.Alternating with the folds are flat furrows 4 and 5. The furrows 4 havean inlet aperture 6 and an outlet aperture 7 for combustion-supportingair which is to be pre-heated. The furrows 5 have an inlet aperture 8and an outlet aperture 9 for exhaust gas the heat from which preheatsthe combustion air. The sheet 1 is inserted in a housing 10 comprisingfour lateral walls, namely two wide walls 11 and two narrow walls 12,which are arranged in the form of a rectangle. The walls 11 are formedwith the apertures 6, 7, 8 and 9. Plate-like end closure members and 16are located near respective corrugated edges 13 and 14 of the sheet 1.Between the edges 13 and 14 and their nearby members l5 and 16 there aresituated plate-form sealing elements l8 and 19 which consist of afelt-like refractory material, for example aluminium oxide, and whichpress firmly on the respective edges 13 and 14. Those surfaces of thesealing elements 18 and 19 which are in contact with the edges 13 and 14can be reinforced by coating with a hardening refractory composition,for example a special cement. The sealing elements 18 and 19 can beprovided with an internal insert, such as the insert 17 for the element19, consisting of a refractory wire gauze, to give them increasedstrength. Between the sealing element 18 and the member 15 there issituated a corrugated leaf spring 20 which through an intermediate plate21 makes the sealing elements 18 and 19 press firmly on the edges 13 and14 of the sheet 1. The spring 20 is situated near the colder corrugatededge of the sheet 1 that is to say at that end of the housing 10 atwhich the air inlet aperture 6 and the exhaust gas outlet aperture 9 aresituated. The member 16 is securely connected to the walls 11 and 12 ofthe housing 10 whereas the member 15 is detachably connected thereto.The connection of the member 15 to the housing 10 can be made, as FIG. 4shows, by a bayonet-type joint wherein pins 22 secured to the member 15engage in angled grooves 23 in the walls 11 and lock the member 15 inthe closed position. This kind of closure permits easy removal of themember 15, which for this purpose must be capable of longitudinaldisplacement. The folded plate 1 can be cleaned when removed from oreven while remaining in the housing 10. Adjoining the apertures 6, 7, 8and 9 are inlet and outlet ducts which have been left out of thedrawings in order to make them easier to read. They can be welded forexample to the walls 11 of the housing 10 or secured there in some otherway. The non-corrugated edges of the sheet 1, as FIG. 5 shows for oneedge 24, are embraced by the walls 12 together with in each case a lipplate 25 with the interposition of a sealing element 26 of U-shapedcross-section embracing the edge 24. The sealing element 26 can consistfor example of a paintable refractory substance such as, for example, aspecial cement which subsequently hardens. In this case it has to berenewed each time the sheet 1 is taken out of the housing. The parts 11,12 and 25 are welded or soldered together at the region 27, but mayinstead be connected together in another way, for example bybeading-over. The paths followed by the heat-exchange media are shown inthe drawings, more particularly FIG. 2, by the arrows A for thecombustion air and the arrows B for the exhaust gas. It will be notedthat the two media streams are substantially in counter-flow withrespect to each other.

The drawings are not representative of the actual dimensions of thesheet 1 if the apparatus is an air preheater. In such a case, thefurrows 4 and 5 are much narrower than shown here. l-l.5 mm and 0.4 mmrespectively are preferred dimensions for the furrow width h (FIG. 3)and the sheet thickness d. To maintain the width dimensions of thefurrows 4 and 5 and to improve the dimensional stability of thecorrugated sheet 1, the sheet 1 can be formed with indentations toprovide corresponding space-maintaining projections 28. The dimension ofthe sheet 1 in the direction of the folds 2 and 3 can also be muchgreater than is shown here.

Referring to FIGS. 6 and 7, to maintain the width dimensions of thefurrows 4 and 5, the folds 2 and 3 are pressed inwards, forming portions29 and 30 which are widened transversely to the folds and which contactone another at the regions 31 and 32 and thus define the spacing of thecorrugations of the sheet 1. The number and positions of the portions 29and 30 depend on the length of the furrows 4 and 5 and the size of theapertures 6 to 9. Conveniently rows of widened portions 29 or 30 areprovided along all horizontal edges of the housing 10. To produce theportions 29 or 30, a spacer plate 33 the thickness of which equals thedesired width of the furrow is inserted into each furrow 4 or 5, as FIG.7 shows. The spacer plates 33 leave the folds free so that they can bepressed to a widened shape locally with the help of a bar-shaped tool34. In this operation, the sheet 1 is held in position by the spacerplates 33 since the spacer plates are clamped together by clampingscrews 35 and nuts 36 through U- members 37. As FIG. 7 shows, thebar-shaped tool 34 can have a rectangular profile. However, it caninstead have a wedge-shaped or semi-circular profile. It is hardened andground. The height 11 thereof is slightly greater than the necessarypress-in depth, owing to the resilience of the sheet 1. This depthdepends on the furrow width, the uniformity of the folds and thethickness of the sheet 1, and is determined by tests. The pressinginoperation is carried out on a hydraulic press the ram of which can bemoved in a finely controlled manner.

which serve to maintain the width of said furrows.

1. In a method of producing a heat exchanger comprising a corrugatedmetal sheet which forms a heat transfer wall, the steps of insertingspacers into furrows alternating with folds of said sheet but so as toleave said folds exposed, clamping together said spacers with theinterposition of said sheet, and pressing portions of said folds inwardssimultaneously with a bar-like tool to form at said folds projectingportions of said sheet which serve to maintain the width of saidfurrows.